1. Field of the Invention
The present invention relates to a disk cartridge for accommodating a disk-shaped recording medium, and more particularly, to a disk cartridge having double structure suitable for accommodating a hologram media disk.
2. Description of the Prior Art
In recent years, a hologram media disk comes to the fore, which disk has considerably large information storage capacity as compared with a conventional disk-shaped recording medium such as a CD (compact disk) or a DVD (digital video disk). The hologram media disk also has an advantage of being capable of simplifying a drive system of a recording and reproducing apparatus since it has no need to rotationally drive the disk at a high speed.
In digital hologram recording by using this hologram media disk, information is recorded at an interference point in a thickness direction of a recording layer utilizing interference of a recording beam and a reference beam, and the information recorded at this interference point is read out by the reference beam, unlike the digital recording using the conventional disk-shaped recording media. This method makes it possible to record and reproduce a large amount of information at a high speed, since the method can record and reproduce a large amount of data by one light irradiation.
The recording media used for the digital hologram recording is constructed by sandwiching a hologram material between two disk substrates. Conventionally, this hologram material is composed mainly of inorganic single crystal called as photorefractive crystal such as lithium niobate single crystal, and therefore, has problems of being expensive and difficult to process. However, an organic hologram material including a photo polymerization material as a base, which has been investigated in recent years, can be expected to make dramatic improvement concerning the above described problems. More specifically, as an organic hologram recording material, a material which is made by mixing and diffusing the photo polymerization material serving as a recording material into a polymer matrix serving as a support medium is used, and when producing the recording media, this material is diluted by a solvent and coated on a substrate as a coating material, or this material is worked into a film form and then attached on a base material.
However, the hologram material using a photosensitive copolymer is easily deteriorated by exposure to external light, and therefore, in order to putting a recordable or rewritable hologram media disk into practical use, it is necessary to block the external light by accommodating the hologram media disk in a disk cartridge with light blocking effect.
Conventionally, in order to protect the disk-shaped recording media from contamination and mechanical breakage in a VD (video disk) and a MD (minidisk), for example, an art of accommodating the disk-shaped recording media into the disk cartridge has been known. For example, in the specification of U.S. Pat. No. 5,526,337, there is proposed a method for securing light blocking effect during storage, by accommodating hologram media in the cartridge having light blocking effect, and by opening and closing a drive shaft insertion aperture and a head access aperture by using a shutter when attaching and detaching the hologram media to and from a recording and reproducing apparatus.
Also, JP-A-8-55456, for example, discloses a method for making the cartridge structure double to enhance dustproof property. Alternatively, it is proposed to provide the hologram media by using a cartridge in the same shape as a 5.25 type MO cartridge of ISO.
The applicant of the present invention also has proposed a disk cartridge having double structure, for accommodating disk-shaped recording media, which includes: an inner case having an inner head insertion aperture and an inner spindle insertion aperture; an outer case located outside in a thickness direction of the inner case and having an outer head insertion aperture provided at a position overlaying the inner head insertion aperture and an outer spindle insertion aperture provided at a position overlaying the inner spindle insertion aperture; and a shutter slidably disposed between the inner case and the outer case to open and close these insertion apertures. The disk cartridge has been patented (Japanese Patent No. 3430184).